Oilpan: prefer eager finalization over prefinalizers.

Source/core/dom/MutationObserver.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 42 matching lines @@
 typedef unsigned char MutationObserverOptions;
 typedef unsigned char MutationRecordDeliveryOptions;
 
 using MutationObserverSet = WillBeHeapHashSet<RefPtrWillBeMember<MutationObserver>>;
 using MutationObserverRegistrationSet = WillBeHeapHashSet<RawPtrWillBeWeakMember<MutationObserverRegistration>>;
 using MutationObserverVector = WillBeHeapVector<RefPtrWillBeMember<MutationObserver>>;
 using MutationRecordVector = WillBeHeapVector<RefPtrWillBeMember<MutationRecord>>;
 
 class MutationObserver final : public RefCountedWillBeGarbageCollectedFinalized<MutationObserver>, public ScriptWrappable {
     DEFINE_WRAPPERTYPEINFO();
-    WILL_BE_USING_PRE_FINALIZER(MutationObserver, dispose);
 public:
     enum MutationType {
         ChildList = 1 << 0,
         Attributes = 1 << 1,
         CharacterData = 1 << 2,
 
         AllMutationTypes = ChildList | Attributes | CharacterData
     };
 
     enum ObservationFlags  {
@@ skipping 15 matching lines @@
     void observe(Node*, const MutationObserverInit&, ExceptionState&);
     MutationRecordVector takeRecords();
     void disconnect();
     void observationStarted(MutationObserverRegistration*);
     void observationEnded(MutationObserverRegistration*);
     void enqueueMutationRecord(PassRefPtrWillBeRawPtr<MutationRecord>);
     void setHasTransientRegistration();
 
     WillBeHeapHashSet<RawPtrWillBeMember<Node>> getObservedNodes() const;
 
+    // Eagerly finalized as destructor accesses heap object members.
+    EAGERLY_FINALIZE();
     DECLARE_TRACE();
 
 private:
     struct ObserverLessThan;
 
     explicit MutationObserver(PassOwnPtrWillBeRawPtr<MutationCallback>);
     void deliver();
     bool shouldBeSuspended() const;
 
-    void dispose();
-
     OwnPtrWillBeMember<MutationCallback> m_callback;
     MutationRecordVector m_records;
     MutationObserverRegistrationSet m_registrations;
     unsigned m_priority;
 };
 
 } // namespace blink
 
 #endif // MutationObserver_h